1. Field of the Invention
The present invention relates to a liquid supply device and an image forming apparatus, and more particularly to a liquid supply device and an image forming apparatus using the liquid supply device suitable for supplying a liquid for ejection to a multiple head formed to a long dimension by joining together ejection heads having nozzle rows.
2. Description of the Related Art
In the field of inkjet printers, a composition using a line head having a nozzle row of a length corresponding to the full width of the recording medium (a so-called “full line head”) is known in order to achieve high-speed printing, or the like. In general, when an inkjet head is formed as a line head, it becomes difficult to supply ink along a single long dimension. Therefore, it has been thought to improve liquid supply performance by joining together short heads in order to form a long dimension head, and dividing up the flow path to correspond to each short head unit.
In this case, if supply pipes are formed in parallel for the head units from a main tank forming a liquid supply source, then it is necessary to provide the same number of supply pipes as the number of heads, and this gives rise to layout problems. As a means for avoiding such problems, it has been thought to branch off-the-supply tubes at intermediate positions.
In this respect, Japanese Patent Application Publication No. 10-244681 discloses flow path connection configurations for cases where there are a plurality of nozzle unit elements (short heads), and respective connection configurations involving serial arrangement, parallel arrangement or a combination of these arrangements. However, Japanese Patent Application Publication No. 10-244681 simply proposes connection methods, and does not disclose which flow path configuration would be suitable under which conditions.
Japanese Patent Application Publication No. 2003-118135 discloses a method where, in order to supply liquid to a plurality of heads from one main tank, the tank is connected to the heads by repeated branches based on two-branch joints. However, in the case of Japanese Patent Application Publication No. 2003-118135, it is necessary to provide repeated branches in a symmetrical fashion in order to equalize the pressure loss at each print head. Consequently, there are very significant restrictions on the layout. Moreover, the method described in Japanese Patent Application Publication No. 2003-118135 also entails a problem in that it cannot be applied to an odd number of heads.
Japanese Patent Application Publication No. 2000-153622 discloses a composition in which a flow path resistance altering device is provided in the course of a tube which connects a cap unit used in a cleaning operation for restoring the ejection performance of an inkjet head to a plurality of pumps. Japanese Patent Application Publication No. 2000-153622 relates to flow paths for ink removal, and it achieves reductions in maintenance and initial refill times, simplification and improved performance of the pump unit, and compactification of the apparatus. However, it does not describe the features of a flow path system for supplying ink to a plurality of heads.